Energy decoupling of closely spaced radar antenna horns



June 20, 1961 F. s. ATCHISON 2,989,747

ENERGY DECOUPLING OF CLOSELY SPACED RADAR ANTENNA HORNS Filed May 21, 1952 INVENTOR FRED 5. ATGH/SO/V ATTORNEY}? 2,989,147 DEJGQUPLING QF GLQSELY GE RADAR ANTENNA HORNS Fred S. Atchison, Bethesda, Md., assignor to the United States of America asre 'ir'esente'd by theSecretary of the Navy L FiledMay 2'1, 19'52,'Ser. No. 289,185 4 Claims. (Cl. 343-076) (Granted under Title '35, US. Code (1952), sec. 266) The present invention relates generally to an improvement in radio" antennae, and is more' particularly' concerned with a means for decoupling closely spaced radio antennae feeds.

In the art of locating or tracking objects by means of transmitting radio waves and receiving the echos thereof as reflected from the objects, it has been found desirable in certain applications thereof to utilize a plurality of closely spaced antenna energy feeds for directionally transmitting and/or receiving the radio waves. An example of such a system utilizing an antenna having two closely spaced energy feeds cooperating with a parabolic energy reflector to transmit and to receive echo waves directionally is described in the application of Fred S. Atchison, Serial Number 294,113, filed on June 17, 1952, now abandoned. When utilizing two closely spaced energy feeds for alternate energy reception, wherein each feed is sequentially blocked and opened to energy reception alternately with the other feed, a portion of the energy received by the antenna may enter the blocked feed, be reflected by the block back out of the feed, and then couple into the open feed to distort the signal there received. The disadvantages of such energy coupling and resultant signal distortion are apparent, and it is therefore an object of the present invention to provide an antenna structure enabling the use of a plurality of closely positioned energy transmitting and/ or receiving feeds by minimizing or substantially reducing the energy coupling that would be normally had therebetween. Other objects and advantages of the present invention will become apparent from a consideration of the following detailed description thereof, made in conjunction with the accompanying drawings in which:

FIG. 1 is a front view of an antenna utilizing two closely spaced energy feeds and embodying the present invention; and

FIG. 2 is a side view of the antenna shown in FIG. 1.

Referring to the drawings, numerals and 11 generally indicate a pair of electromagnetic microwave antenna feeds, representing the ends of two waveguides 12 and 13 respectively. If desired, the ends of the feeds 10 and 11 may be provided with the energy transmitting plugs -14 and 15 respectively, as is common in waveguides. A parabolic reflector 19 may be provided which cooperates with the feeds 10 and 11 to accomplish a directional concentration of energy transmitted from the feeds, and a directional preference for energy reception by the feeds.

The foregoing description of the feeds 10 and 11 is directed to those portions of the antenna shown in the drawings which are conventional in microwave directional transmission and reception. And in addition to the above-described elements, the present antenna includes the inside plate 18 and the two outside plates '16 and 17, all formed of electrically conductive material. The inside plate 18 is positioned between and electrically connects the two feeds to provide a short circuit therebetween for the energy conducted therethrough, and is positioned along the feeds so that its side nearest the ends 12a and 13a of the waveguides 12' and. 13' is set back therefrom by a distance substantially equalto one quarter of the wavelength of" the energyconducted Patented June 20, 1 961 ice through the feeds. In accordance with transmission line' 7 theory, by providing this e'ner'gy'short circuit at a distance of one quarter wavelength back from the ends of the Waveguides, the gap between the ends of the two feeds appears as an open circuit to the energy leaving either (feed. A choke is thus provided between the two feeds 10 and 1 1 which effectively reduces the energy coupling between the two feeds, and substantially minimizes the coupling that would otherwise be obtained.

It has been found that the coupling between the two feeds may be further reduced by aflixing the plates 16 and 1-7 to the outside 'sidesof the two feeds, '10 and 11 opposite from the inside plate 18, and positioning them to project from the ends of the waveguides. The reason for the decoupling effect had by the plates 16 and 17 is not understood, but it has been found empirically that if the plates 16 and 17 are positioned to project from the ends of the waveguides by 0.11 inch, they are effective in further diminishing the coupling be tween two waveguides when the wavelength of energy employed is approximately 1.2 inches.

Thus by the proper positioning of the electrically conductive plate 1 8 between the two closely spaced feeds 10 and 11 as above-described, the energy coupling had between the two feeds is substantially reduced to enable a more accurate energy signal transmission or reception by the feeds; and in addition, by providing the two plates 16 and 17 on the outside sides of the waveguides opposite from the plate 18, and projecting by the appropriate amount from ends thereof, as indicated above, still fur ther decoupling of the feeds may be obtained. By employing the practices taught by the present invention and when utilizing radio energy having a wavelength of approximately 1.2 inches, it has been found that the energy feeds may be positioned as close to each other as 0.6 inch between centers without incurring any more than a relatively insignificant amount of energy coupling between the feeds. Although the present invention is herein specifically described in its application to a twowaveguide antenna, it is apparent that it may be readily adapted to and modified to apply to more than two waveguides. Therefore, the foregoing detailed description of one embodiment of the present invention is presented merely by way of example, and modifications of the invention within the spirit and scope thereof, as defined by the appended claims, will be apparent to those skilled in the art and are Within the contemplation of the present patent.

The invention described herein may be manufactured and used by or for the Government of the United States of America for government purposes without the payment of any royalties thereon or therefor.

What is claimed is:

1. An antenna for electromagnetic microwave transmission or reception comprising two closely spaced waveguides, an electrically conducting plate interposed between said waveguides and electrically connecting them, said plate being located a distance back from the ends of the waveguides substantially equal to one quarter wave length of the energy conducted through said waveguides, and two additional plates of electrically conducting material positioned on the outside portion of each waveguide substantially oppcsite from the portions of the waveguides housing :the first-mentioned plate and extending beyond the ends of said waveguides, thereby providing two closely spaced energy transmitting or receiving waveguides having a small energy coupling therebetween.

2. An antenna for electromagnetic microwave transmission or reception comprising two closely spaced energy feeds, an electrically conducting plate interposed between said feeds to connect them electrically, said plate being located a distance back from the ends of said feeds subg 3 c stantially equal to one quarter wavelength of the energy conducted therethrough, and additional plates of electrically conducting material positioned on the outside portions of said feeds substantially opposite from the por-.

tions thereof housing said first-mentioned plate and extending beyond the ends of said feeds, thereby providing two closely spaced energy transmitting or receiving feeds having a small energy coupling therebetween.

3. An antenna for radio energy transmission or reception comprising two closely spaced energy feeds, and an electrically conducting plate interposed between said feeds to connect them electrically, said plate being located a distance back from the ends of said feeds substantially equal to one quarter wavelength of the energy conducted therethrough, thereby providing two closely spaced energy transmitting or receiving feeds having a small energy coupling therebetween.

a. 2,9s9,747 r References Cited in the file of this patent UNITED STATES- PATENTS 2,283,935 King' May 26, 1942 2,412,867 Briggs a a1. Dec.'17, 1946 2,486,620 Van Atta Nov. 1,1949 2,591,486

' Wilkinson Apr. 1 1952 

